1 Design of experiment to determine the HAZ hardness of ASTM A299 Steel Indraroop Ghosh Dastidar*, Ananda Ghoshal, Subanta Neogi, R N Ray Department of Metallurgical and Materials Engineering, National Institute of Technology, Durgapur, West Bengal - India - 713209 *Corresponding author: Email address:- ighoshdastidar7@gmail.com ABSTRACT Purpose: The aim was to obtain an empirical relationship between the HAZ (Heat Affected Zone) hardness of ASTM A299 Steel and the weight percentage composition of its different constituents. Design/Methodology: The compositions of the seven main components of ASTM A299 Steel were varied within a certain range and different designs of experiments were performed. For each set of composition the HAZ hardness in as-welded condition after cooling from 800 0 C-500 0 C were obtained using a computational tool named WeldSoft. The results for each design of experiments were noted and analyzed using regression analysis to obtain the corresponding empirical relationship and the goodness of fit. Findings: It was found that the one twenty seventh fraction of the three level full factorial design and the face centered central composite design give the best goodness of fit and the number of experiments done in each case were not high, so this two designs are considered as the best design. Practical implications: By performing different designs of experiments it can be found out which design gives a highly accurate estimate with less number of experiments. In that way the need for performing all experiments is eliminated, the results of all other experiments can be found out from the estimate obtained and the process becomes very economical. Keywords:- HAZ Hardness, Factorial Designs, Goodness of fit. 1. Introduction Design of Experiments In general usage, Design of Experiments (DOE) is the design of any information-gathering exercises where variation is present, whether under the full control of the experimenter or not. Experimental designs have found broad applications in many disciplines. It is a critically important tool in the engineering world for improving the performance of a manufacturing process. It has also extensive applications in the development of new processes. The application of external design techniques early in the process development can result in a. Improved process yields b. Reduced variability and closed conformance to nominal or target requirements. c. Reduced development time d. Reduced overall costs Experimental designs may also play a major role in engineering design activities where new products are developed and existing one are improved. Some applications of experimental design in engineering design include a. Evaluation and design of basic design configurations. b. Evaluation of material alternatives. c. Selection of design parameters so that the product will work well under a wide variety of field conditions, that is, so that the product is robust. d. Determination of key product design parameters that impact product performance. The use of experimental design in these areas can result in products that are easier to manufacture, products that have enhanced field performance and reliability, lower product cost and development time [1]. HAZ(Heat Affected Zone) The heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which has had its microstructure and properties altered by welding or heat intensive cutting operations.